1. Field of the Invention
The present invention relates to an exhaust gas cleaning device for an internal combustion engine of a motorcycle, adapted to supply the secondary air to the exhaust system of an internal combustion engine mounted on a motorcycle while controlling the supply so as to clean unburnt components in exhaust gas.
2. Description of the Prior Art
Such an exhaust gas cleaning means for an internal combustion engine of the above-mentioned type is generally known as adapted to supply the secondary air to the exhaust system of the engine in order to remove noxious components contained in the exhaust gas in the exhaust system. The exhaust gas cleaning means of this type, however, has such a disadvantage that when a motorcycle is driven while such a starting aid as a choke valve, a by-starter or the like is being actuated in warming-up of the engine, a relatively large amount of exhaust gas unburnt components, such as HC, CO and the like, discharged from the engine actively react with the secondary air supplied to the exhaust system, so that the exhaust pipe in the exhaust system becomes relatively high in temperature in low-speed operations in which cooling by means of the outside air such as wind resulting from travelling cannot be much expected, causing discoloration of the film, such as Cr plating, deposited on the outer surface of the exhaust pipe, resulting in deterioration of the commercial value.